Ice vs Rock - freeze-thaw, glaciers, U-shaped valley, abrasion
Ice vs Rock
freeze-thaw, glaciers, U-shaped valley, abrasion
Erosion and Weathering Unit
Have you ever tossed a plastic bottle full of water into the freezer? When you opened the freezer a few
hours later, you might have found a big mess. The bottle had broken. Water leaked everywhere and
froze. Ice is pretty powerful stuff. It can rip apart plastic. It can break rock, just like wind and water.
Bump-bump. When your bicycle tire hits a pothole in the road, you get a first-hand look at how ice can
break rock. Rain or melted snow soak into small cracks or holes in the road. When it gets freezing cold at
night, that water becomes ice. Then it's just like what happened to the bottle in your freezer. The ice
expands and takes up more space than the water did, breaking the road apart. The next day, as the road
warms up, the ice melts and creeps deeper into the cracks, only to turn back to ice when it gets cold
again. Freeze-thaw is when water becomes ice as the temperatures dip below freezing, then turns to
water again as the day heats up and repeats this over and over.
In some parts of the world, it is cold or freezing all year around. The snow does not melt much, so it builds
up over time. This snow becomes heavier and heavier, pushing down on the layers of snow on the
bottom. Think about what happens when you forget about that banana in your bag and put your books on
top of it. Squish! The same thing happens with the snow. The snow on the bottom gets so squished that
it turns to ice. Glaciers are slow moving rivers of ice formed from years of snow build up. They flow like
slow rivers, but move so slow that you cannot see it.
Glaciers are like big bulldozers. They have a lot of power to change the shape of the land. This is
because they are made up of more than just snow and ice. At the bottom of the ice sheet, there are rocks
that have been frozen into it. This makes the ice like the roughest sandpaper you have ever seen. When
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Ice vs Rock - freeze-thaw, glaciers, U-shaped valley, abrasion
the ice flows down the hill, those rocks in the ice grind away at the rock under the ground, just like
sandpaper grinds and smooths rough wood. Abrasion is when something grinds away at something
else. The glacier rubbing against the ground is an example of very strong abrasion.
When glaciers flow downhill, they often follow the zigzag paths that streams have carved. Most valleys
made by streams look like the letter V. That is because the water only wears down at the bottom of the
valley, where the water is flowing. Ice works in a different way. Instead of just pushing dirt from the
bottom of the valley, the ice grinds against the sides too. It works more like a spoon. It scoops out the
valley, making it look like the letter U. U-shaped valleys are valleys shaped by glaciers with steep sides
and wide bases.
Ice is powerful stuff. It can burst your water bottle. It can break up the road. Great flowing ice sheets can
grind up the land. In the battle of rock versus ice, ice wins, hands down.
References:
"All About Glaciers." National Snow and Ice Data Center, 2013. <https://nsidc.org/cryosphere/glaciers>
Ferguson, William. "Ice Core Data Help Solve a Global Warming Mystery." Scientific American, March
2013. <http://www.scientificamerican.com/article/ice-core-data-help-solve/>
"Glacier." UXL Encyclopedia of Science. U*X*L, 2001. Science In Context.
<
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odId=SCIC&windowstate=normal&contentModules=&display-query=&mode=view&displayGroupName=Re
ference&limiter=&currPage=&disableHighlighting=false&displayGroups=&sortBy=&search_within_results=
&p=SCIC&action=e&catId=&activityType=&scanId=&documentId=GALE%7CEJ2644300497&source=Boo
kmark&u=k12_science&jsid=b81adb61d4e759b38e093fd822373042 >
"Global Sea Level." NASA, July 2013.
<http://www.nasa.gov/topics/earth/features/pia16294.html#.U8mwLLFeZzc>
“Sea Level” NASA Climate Kids, 2013 <http://climatekids.nasa.gov/health-report-sea-level/>
"Sea Level Rise: Ocean Levels Are Getting Higher -- Can We Do Anything About It?" The Ocean. National
Geographic, 2013. <http://ocean.nationalgeographic.com/ocean/critical-issues-sea-level-rise/>
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